Process of producing iron sheets for laminated electric transformer cores



Patented Feb. 4, 1941 PROCESS OF PRODUCING IRON SHEETS FOR LAMINATEDELECTRIC TRANSFORMER CORES August Canzler, Bochum, Germany, assignor tothe firm Eisen und Hiittenwerke A.-G.,

Bochum, Germany No Drawing. Application September 7, 1938, Se-

rial No. 228,868.

1 Claim.

In the usual process of producing the sheets from which laminatedelectric transformer coils and dynamo armatures are built up the sheetsare produced by hot-rolling, then pickled for removal of scale, washedand neutralized by treatment with lime, and washed and dried. Thesepreliminaries are followed by cold-rolling for smoothing the surfaces,and this in turn is followed by annealing, which again produces scalenecessitating treatment for removal thereof, generally by a bath ofhydrochloric acid, after which the sheets are washed with water, treatedwith lime or soda, and finally polished and dried.

The second production of scale in the course of these operations,following the annealing by heat, not only involves the after-treatmentdescribed but results in some loss of material. To avoid this it hasbeen proposed to give the sheets a protective coating before they areannealed, for example a coating of nickel, chromium, tin, zinc,aluminium or other metal, but in practice this method is not workable.An even metal coating suitable for the purpose can only be produced byan electrolytic process, which is too expensive, and the quality of thesheets from the electromagnetic point of view is deteriorated by thecoating of another metal. Owing to the silicon content of the iron themetal coating tends to produce, on the surface, a mixture of siliclcacid and metal oxide, which must be removed.

It has also been proposed to coat the sheets with water-glass or with amixture of waterglass and powdered tin, but tests have shown that thewater-glass tends to roughen the surfaces of the sheets, due to depositsleft thereon, and the coating does not eliminate risk of rust. Moreover,the water-glass makes it more diificult to apply insulation between thesheets.

In some processes of manufacture articles which require annealing arefirst given a coating composed of a halogen salt of an alkali mixed witha base such as calcium fluoride or calcium chloride. This method is notsuitable for transformer sheets, because aspecial cleansing process isnecessary for removing the coating, and the surfaces of the sheet wouldthereby be damaged.

According to my invention the sheets produced by hot-rolling and thenpickled and polished are,

In Germany December 4,

the formation of scale.

is particularly suitable,

tri-sodium phosphate.

It will be seen from A phosphate solution especially a solution of theabove statement of my invention that the operatives involved may becarried out in the following order:

(a) Hot-rolling, following by pickling and polishing.

(b) Coating with tri-sodium phosphate or equivalent alkali, and drying.

(c) Cold-rolling for smoothingthe sheets.

(d) Annealing.

If this 'order is varied by cold-rolling the sheets before applying thecoating two drying operations are required, one

after the pickling and polishing or cleaning and one after applying thecoating. stated there is only one The coating may be With the preferredorder first drying operation. applied by dipping the sheets, but it ispreferred to spray them with the solution. The sheets may for thispurpose be caused to travel over or under a transverse series of sprayertubes from which the solution is projected under pressure, a very evencoating being thus obtainable.

An important advantage obtained by the process when the coating isapplied before the cold rolling is that coating then acts as a smoothingagent.

Instead of phosphates I may use other agents precipitated from aqueoussolution, e. g. sodium aluminate.

What I claim as my secure by Letters Patent A process for producing ironsheets with a invention and desire to of the United States is:

silicon content for use in making electric transformer cores, whichconsists in hot rolling the iron to give it sheet form, pickling andcleaning the hot rolled sheets, applying a coating of trisodiumphosphate, and ing and annealing.

then drying, cold rollnuaosr CAN-ZLER.

